Classification

Distribution

Currently understood to be widely-distributed with records existing from parts of Myanmar, Thailand, Laos, Cambodia, Vietnam, Peninsular Malaysia and the Indonesian island of Sumatra.

It thus occurs in several major river drainages including the Mekong, Chao Phraya, Mae Klong, Irrawaddy and Salween, plus countless smaller ones.

It was described from ‘Tenasserim Provinces’ which could refer to any one of five or more modern day states in Myanmar, most likely a former division in the south of the country now known as Tanintharyi Region, and later authors have tended to use Weber and de Beaufort’s (1916) description of Sumatran specimens as reference.

However the fish exhibit differences in colour, patterning and morphology depending on locality and it’s possible that the species as currently-recognised will turn out to represent a complex of closely-related fishes should a detailed study be conducted (see ‘Notes’).

Wild examples are now rare in the trade with the vast majority produced commercially in South East Asia or eastern Europe.

Habitat

Inhabits various habitat-types from well-oxygenated, clear streams with rocky substrates running through forested areas, to still bodies of water such as ponds, ditches and rice paddies.

This species is very peaceful indeed making it an ideal resident of the well-furnished community tank.

Since it places no special demands in terms of water chemistry it can be combined with many of the most popular fish in the hobby including other small cyprinids as well as tetras, livebearers, rainbowfishes, anabantoids, catfishes and loaches, though as always when selecting a compatible community of fishes thorough research is essential and its small adult size must be a consideration.

A community based around species from one of its native countries or river basins would also make an interesting project with possibilities from the Mekong alone including representatives of Acanthocobitis, Annamia, Balitora, Homaloptera, Nemacheilus, Schistura, Sewellia, Lepidocephalichthys, Pangio, Yasuhikotakia, Crossocheilus, Devario, Garra, Rasbora, Glossogobius, Rhinogobius, Glyptothorax, Akysis and Trichogaster.

It’s a schooling species by nature and really should be kept in a group of at least 8-10 specimens.

Maintaining it in such numbers will not only make the fish less nervous but result in a more effective, natural-looking display, while males will also exhibit their best colours as they compete with one other for female attention.

Sexual Dimorphism

Sexually mature females are usually rounder-bellied, slightly less colourful and a little larger than males.

The differences are especially clear when the fish are in spawning condition as the males intensify in colour and the females fill with eggs.

Reproduction

Like many small cyprinids this species is an egg-scattering spawner that exhibits no parental care.

That is to say when the fish are in good condition they will spawn often and in a densely-planted, mature aquarium it is possible that small numbers of fry may start to appear without human intervention.

However if you want to increase the yield of fry a slightly more controlled approach is required.

The adult group can still be conditioned together but one or more smaller, say 20-30 litre containers should also be set up and half-filled with water.

These should be very dimly lit and the base covered with some kind of mesh of a large enough grade so that the eggs can fall through it but small enough so that the adults cannot reach them.

The widely available plastic ‘grass’-type matting can also be used and works very well; alternatively filling much of the tank with Java moss or other fine-leaved plant can also yield good results.

The water itself should be of slightly acidic to neutral pH with a temperature towards the upper end of the range suggested above.

A small power filter can be added initially and this should be positioned so that the flow is directed down the full length of the tank.

When the adult fish are well-conditioned and the females appear full of eggs one or two pairs should then be introduced to each container.

Spawning can be initiated by adding small amounts of cool water every few hours in such a way that the tank is gradually topped up and feeding small amounts of live and frozen foods.

The pair should spawn the following morning. The easiest and quickest way to tell is simply to look at the female. If the fish have spawned she will be noticeably slimmer.

The adults will eat any eggs they find and are best removed after a couple of days at which point the power filter should be switched for a mature sponge-type unit in order to avoid fry being sucked into the mechanism.

Incubation is temperature-dependant to an extent but usually takes between 24 and 36 hours with the young free-swimming a few days later.

Initial food should be Paramecium or a proprietary dry food of sufficiently small (5-50 micron diameter) grade, introducing Artemia nauplii, microworm, etc., once the fry are large enough to accept them.

Doubts remain whether B. albolineata is representative of a single species or a group of similarly-patterned, closely-related fish, and the form from Chantaburi province in eastern Thailand was revalidated as B. pulchra (formerly Danio pulcher Smith, 1931) by Kottelat (2013). The status of the currently invalid Danio tweediei Brittan, 1956 from Kedah state, northern Peninsular Malaysia may also be in question, since fish from that area are clearly identifiable from other forms and have even been misidentified as B. kerri in aquarium literature.

Specimens collected from different areas exhibit clear differences in colouration and patterning, e.g., those from western Thailand tend to show some orange colour in the dorsal half of the body while in central parts of the country the same portion is coloured blue. The length of the central orange stripe which extends from the caudal peduncle can also vary in both thickness and length, even among specimens collected from a single locality.

There is also a natural form from Yunnan province, China (see images) that superficially resembles B. rosea this is unlikely to have been collected for the aquarium trade.

Breeders in eastern Europe have successfully crossed B.albolineata with B. rosea, and some of the fish traded are likely to be hybrids. If you want to avoid these beware of examples with a cheap price tag that show a high proportion of both powdery-blue colouration on the body and red in the ventral and anal fins.

In recent years it’s become commonplace to refer to the stripes on the body and fins of danionins as follows:

– P stripe: or “pigment stripe” is the central, dark, lateral stripe on the body which extends into the caudal-fin in some species. Stripes above it are numbered P+1, P+2, etc. and those beneath P-1, P-2, P-3.
– A stripe: the central stripe on the anal-fin; the proximal stripe (above it) is A+1 and the distal stripe (beneath) A-1.
– D stripe: The submarginal dorsal-fin stripe.

Following Fang (2003) Brachydanio spp. are characterised by the presence of an A stripe on the anal-fin and two or more P stripes on the caudal, plus some internal characteristics such as enlarged nasal lamellae.

The genus has undergone some significant taxonomic reshuffling in recent years following the publication of a series of phylogenetic studies.

Older, molecular, phylogenies tended to agree that it represented a monophyletic group consisting of two major clades; the ‘Danio devario‘ group containing the larger, deeper-bodied species and the ‘D. rerio‘ clade comprising the smaller, slimmer fish.

However in 2003 Fang conducted a more detailed study based on morphological characters which included members of other related genera, and the results suggested for the first time that the genus Danio as previously considered represents a polyphyletic grouping, i.e., not all members derived from a single common ancestor.

The genus name Devario was suggested for the larger species with Danio being applied only to the smaller fish (with the exception of the type species, D. dangila which can grow to around 89 mm SL). Recent molecular studies by Mayden et al. (2007) and Fang et al. (2009) resulted in further changes, with the latter study considering the genus Danio to be composed of three subclades. These were subsequently split into distinct genera by Kottelat (2013), as follows:

The former species D. erythromicron, D. margaritatus, D. choprae and D. flagrans are grouped together in the revalidated genus Celestichthys Roberts, 2007.These exhibit unique body patterning consisting of vertical bars (C. erythromicron, C. choprae, C. flagrans) or light spots (C. margaritatus) and possess either very short barbels or none at all.

The genus Danio contains only the type species, D. dangila, separated on the basis of its larger size and the shape of the caudal-fin, which in adults is only slightly emarginate or even truncate in shape, a feature it shares only with Tinca tinca (the common tench) among other cyprinids.

The remaining species, of which B. rerio is thought to be the most ancient, are included in the revalidated genus Brachydanio Weber & de Beaufort, 1916.

References

Blyth, E., 1860 - Journal of the Asiatic Society of Bengal 29(2): 138-174Report on some fishes received chiefly from the Sitang River and its tributary streams, Tenasserim Provinces.

Kottelat, M., 2013 - The Raffles Bulletin of Zoology Supplement 27: 1-663The fishes of the inland waters of southeast Asia: a catalogue and core bibiography of the fishes known to occur in freshwaters, mangroves and estuaries.